Successive Ionic Layer Absorption and Reaction for Postassembly Control over Inorganic Interdot Bonds in Long-Range Ordered Nanocrystal Films

Abstract

Epitaxially connected assemblies of nanocrystals (NCs) present an interesting new class of nanomaterial in which confinement of charge carriers is intermediate between that of a quantum dot and a quantum well. Despite impressive advances in the formation of high-fidelity assemblies, predicted collective properties have not yet emerged. A critical knowledge gap toward realizing these properties is the current lack of understanding of and control over the formation of epitaxial interdot bonds connecting the NCs within the assemblies. In this work we demonstrate successive ionic layer absorption and reaction (SILAR) to enhance the interdot bonding within the NC assembly. SILAR treatment improved the fraction of interdot bonds from 82% to 91% and increased their width from 3.1 to 4.0 nm. Absorption spectra and charge transport measurements indicate that the effect of postassembly growth on quantum confinement in this system depends on the composition of the SILAR shell material. Increased NC film conductance following SILAR processing indicates that building and strengthening interdot bonds lead to increased electronic coupling and doping in the assemblies. The postassembly film growth detailed here presents an opportunity to repair structural defects and to tailor the balance of quantum confinement and interdot coupling in epitaxially connected NC assemblies.

Electron Mobility of 24 cm2 V−1 s−1 in PbSe Colloidal‐Quantum‐Dot Superlattices

“…The combined effect is an increase in the effective CQD size and the decrease in the superlattice spacing is observable in the absorption spectrum as a redshift of the first excitonic peak. Interestingly, the particle shape in the extreme areas of the sample becomes more cubic, similar to what is occurring in sulfide‐treated PbS CQDs . On the other hand, EDA removes lead‐oleate groups, leaving a naked CQD behind .…”

Structural characterization of a polycrystalline epitaxially-fused colloidal quantum dot superlattice by electron tomography

“…Most of these defects have been observed in 2D epi-SLs (QD monolayers), which are readily imaged by conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). 12,[16][17][18][19][20][21][22][23][24][25][26][27] Transport measurements of 2D epi-SLs show that carriers are localized, and several groups have proposed that missing necks are a primary cause of carrier localization in these materials. 12,18 Furthermore, the electronic coupling of necked QDs is expected to be sensitive to neck polydispersity (length, width, atomic coherence, and faceting) and the number of nearest neighbor QDs.…”

Interfacial Self-Assembly and Oriented Attachment in the Family of PbX (X = S, Se, Te) Nanocrystals

“…The deviations in NC density can be attributed to the relatively broad NC size distribution (±10% by TEM). 12 Deviations in the amount of bonds per NC can be attributed to exhaustion of mobile surface atoms needed to form crystalline necks; 41 the NCs preferably form robust necks with a few neighbors instead of weaker necks with all of them.…”